Valentine’s Day Storm on the way?

The potential weekend storm has become much less likely. A very strong arctic front will move across the south tomorrow night into Saturday, producing some snow flurries and snow showers across Tennessee, North Carolina, and the higher elevations in Northern Alabama, North Georgia and Northern South Carolina.  The front is strong, and this, in combination with the Polar Vortex moving south in NE Canada, will push the low pressure system that would have brought us a potential snowstorm, too far to the South, into the Gulf. Windy and very cold will describe the weather this weekend, as a taste of “real” Winter hits us.  Temperatures in the teens will be common in many areas for Sunday morning, with high temperatures in the thirties and fourties, with some maximum temperatures not getting out of the twenties, in the higher elevations.  The strong high pressure system that is driving the cold into our area will begin to move to the east and northeast Sunday, and into early next week. As the cold air retreats into the Atlantic, an area of low pressure will begin to move into the southern states from the SW US. This will provide overrunning moisture and enough cold air at the surface along with cold air damming down the Appalachians, to allow snow and ice to fall in Northern Alabama, Mississippi, Georgia, most of Tennessee and Western and Central North Carolina on Monday night and Tuesday.  Accumulations look very possible, and depending on the extent of the moisture, some areas could see significant snow and ice totals.  Following this, an opportunity for rain comes back toward the end of next week. Once again cold air damming may be possible, so along with the risk for heavy rain, some may see more Wintry precipitation.

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Winter storm for the Southeast and east coast possible next weekend

My last blog showed images of the changes the models were showing, which would potentially, finally set up a Winter type pattern for the US, with the Polar Vortex(strong arctic low pressure) finally moving from Alaska(where it’s been stationed all Winter) to NE Canada, near Hudson Bay. This is a typical location during northern hemispheric Winter. The models show a strong PNA(top of roller coaster in the western US) with a ridge and cold air sliding down into the US and a change to wintertime conditions.  However, one thing that was missing, was a negative NAO, which would help block the flow from quickly stretching out into the Atlantic. Due to this lack of a block, the flow became too progressive or quick moving, and this caused what was a sharp high pressure ridge to flatten and stretch to the east, allowing the flow to almost take on a zonal(west to east) flow. Until we get somewhat of a -NAO blocking signature into place, I don’t  think we’ll see the cold and wintry conditions lock in for the southern and eastern US. 

However, with a sharp ridge properly positioned in the western US and the polar vortex located in NE Canada, and sliding to the south, the polar vortex could function to keep the ridge in proper position and suppress southern energy and eventually pull the southern energy to the N/NW,  keeping the ridge from flattening too much and causing a potential strong amplification or phasing of the northern and southern air streams toward the end of this week into next weekend. 

With this in mind, we turn to the current model output for this upcoming week and weekend.  Currently, the GFS, Nogaps, DGEX and Canadian computer models are showing the potential for a storm to develop in the Gulf of Mexico and move up the Atlantic coastline. There is a possibility for a phasing of a northern steam system with a piece of energy in the southern stream, which would potentially make this  a very dynamic system, which could strengthen quickly, as it moves from the Gulf to the SE Georgia coast, and bring significant snowfall to the south and up the east coast. Other possibilities are that the southern energy will move more quickly than the northern energy, which may allow for snow on the northern fringes of the system, but a weaker system, or the northern energy moving more quickly than the southern energy, causing the system to move north into the SE US and up the Appalachians, giving the southern US heavy rain, followed by a possible changeover to snow.  At this point, all possibilities are equally likely.  The GFS, DGEX, Nogaps, and Canadian models are all showing the possibility of a phasing system, or at least a decent snowmaker from the southern Appalachians region up the east coast. I am attaching images.

After this, it appears blocking may finally set up and provide a much, much colder last half of February. One thing to note is that the Polar Vortex split and movement to NE Canada was a result of a stratospheric warming event, which has now caused extensive cold into Europe. Similar patterns, such as took place in 1985, allowed record cold into the US not long after a similar outbreak in Europe. The potential is there for record breaking cold after 2/15. I’ll keep you updated.

GFS model at 7pm this upcoming Saturday, showing the Gulf of Mexico Low pressure areas developing and moving off of the Georgia coast by 1am on Sunday. Note the high pressure ridge(green) in the western US and the flow coming south and then bending back to the northwest, around the polar vortex(low up in NE Canada at top of purple area). Another image shows the blue freezing line at 5000ft altitude, and associated snowfall north of that line.

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Models show potential for Winter in the South and East, Ice, Snow next weekend and beyond…..

With the potential change to a positive PNA pattern, bringing cold air and deep troughing to the eastern US, we also see the GFS Model reflecting a strong upper level low developing and rolling across the southern US, potentially bringing snow and ice to the southern US. See attached(courtesy of Instant weather maps.com):

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This image shows the cold temperatures at the 5000 foot level up in the atmosphere, which would support frozen precipitation. See attached(coutesy of Instant weather maps.com):

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This map shows the positive PNA, with a high pressure ridge in the west, and the cold troughing in the east. The Canadian model is also showing a potential wintry precipitation event of next weekend into early the following week, with a colder pattern. The second image shows the 5000 foot temperatures on 2/5(courtesy of Instant weather maps.com):

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This image(courtesy of raleighwx.net) shows the cool colors in Alaska, which represent the polar vortex still located in Alaska. This kills any transport of cold air from Canada into our area. The next image shows the model depiction of the forecast for the 11-15 day period. Notice how the warm colors now appear in Alaska, showing the vortex replaced by a high pressure ridge. This is a positive PNA and promotes cold transport into the US(down the roller coaster). All models show this now:

 

 

 

 

 

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Winter, finally??

This has been as much of a “non-Winter” as we’ve seen in many years. Last Winter season’s -NAO, + PNA and -AO, which promotes ridging in an ideal location of the intermountain western US, movement of cold arctic air into the US, and blocking of cold air into the eastern US, has been absent this Winter season.  Instead, a very strong low pressure vortex has been locked into Alaska, preventing the development of a +PNA(no ridging in the mountain west, allowing cold air to flow down from Canada).  Please see attached image, showing the results of a positive and negative AO, PNA and NAO.  I have been caught by surprise, by the turn of events. Also, second year La Nina’s sometimes have led to cooler Winter temperatures in the eastern US, IF the atmospheric indices function properly. Obviously, that hasn’t worked out this Winter. 

Where do we go from here?  It appears that, FINALLY, we are seeing consensus among the computer models of a developing +PNA, and in conjunction with a -AO(see images attached), we should see a high pressure ridge build up into Alaska over the next 3-5 days, replacing the powerful low pressure vortex that has been located there since November. This should provide a path for cold air to come down into the eastern US, and should form a sharp trough into the eastern US, potentially leading to a cutoff upper level low pressure system in the southern US, or potentially, a cold air damming event, for the end of the upcoming week, as a strong high pressure cell moves into the northeastern US, funneling cold air down the Appalachians, into NC, upstate SC and NE GA.(see attached images)

From there, the GFS model, European model, and Canadian model, all show the same configuration lasting through at least the first 15 days of February, providing potentially multiple opportunities for Wintry precipitation in the southern and eastern US.  The lack of a -NAO(see image attached), in combination with the subtropical jetstream coming across from the SW US, argues for storms coming across the southern US and out to sea.  At the least, this pattern should provide for colder than normal temperatures for February, after being 5 degrees over normal for December and January.  I am including model depictions of the potential upcoming upper level low pressure and CAD(icestorm potential) scenarios that are showing up for next weekend, as well as the +PNA(roller coaster). 

I’ll keep you updated, but I think we need to look for Winter time coming up after a mild to warm first half of the week.

Image of positive PNA. Notice the warm colors over the western US and into Canada, which depicts the high pressure ridge and the cool colors over the eastern and southern US, which depicts a low pressure troughing area. This corresponds to cooler than normal temperatures for the east and south(courtesy of State of North Carolina Climatology Office).

 

The next image reflects a negative AO(Arctic Oscillation). This promotes movement of air from the Arctic area into the US. Notice the cool blue colors representing cold air(courtesy of State of North Carolina Climatology Office):

This image depicts a -NAO(North Atlantic Oscillation), which is not present heading into February(courtesy of NOAA airmap). Note how cooler air and troughing occur in the eastern US, along with cooler temperatures:

 

 

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Cold and maybe a few snowflakes on the way. Icestorm for parts of the south??

After the rainfall for many parts of the southeastern US, we can look forward to a change back to more wintry conditions.  A very strong Arctic front will pass through the area and move down through the peninsula of Florida tomorrow night into Friday morning. We’ll see an area of light rain develop just ahead of the front, and that precipitation will transition to light snow for areas in northern Alabama, Georgia, Tennessee, northern South Carolina and central and western North Carolina tomorrow afternoon through Friday morning. Some areas(especially higher elevations) should see accumulating snowfall. Light dustings might even accumulate into north central Alabama, and Georgia.  Along with the snowfall, we can expect very windy and very cold conditions beginning tomorrow afternoon and gradually moving from northwest to southeast, eventually covering the SE US. Attached is a map from the NAM(North American Mesoscale) computer model which shows the light rain and snow(behind blue freezing line at 850mb, 5000ft) at 7pm tomorrow night.  High temperatures for Friday will be in the 30’s and 40’s down into south Georgia, Alabama, South Carolina, Tennessee and North Carolina(20’s in the mountains), and dropping into the 50’s into central Florida.  Frost and freeze conditions could reach into north central Florida by Saturday and Sunday mornings.  Temperatures should moderate some on Saturday and Sunday, but still remain quite cold. Another clipper type low pressure system should drop down into the Kentucky, East Tennessee and North Carolina areas on Sunday, bringing another chance of flurries and snowshowers. 

Next week, the high pressure area bringing us the cold/cool air, will slowly move off of the Atlantic coast. However, as it does, another cold front will move in and the combination of flow around the departing high pressure system and the uplift/moisture from the incoming cold front will bring overrunning into Mississippi, Alabama, Tennessee, and eventually Georgia and the Carolinas, for late Monday night through Tuesday night.  As this moisture moves in and the high pressure departs, easterly to northeasterly flow will set up in the favored CAD(cold air damming) areas of the Appalachians, from North Central North Carolina down to NE Georgia. IF the moisture arrives early on Tuesday, the evaporational cooling could lead to freezing rain for these areas, until warm air advection turns the freezing rain to plain rain by Tuesday afternoon.  In some insituational CAD scenarios such as this it is extremely hard to scour out the low level cold, and significant icing develops.  One other thing to consider is that the computer models often underestimate temperatures related to low level, cold, dense arctic air that funnels down the eastern slopes of the Appalachians.  It’s more likely this will just be a very cold rain for these areas, following a brief period of sleet. For the rest of the Southern US outside of the CAD areas, look for a cool rainy Tuesday. After this cool to cold conditions for the remainder of next week.

The longer range looks like we may see a return to  milder conditions, as we get into a zonal flow where mild Pacific air flows into our area from January 20-27.  I’ll update more on that in the next update.  Keep in mind an upper level low pressure system could impact us at any time between now and the end of February, which could bring surprise snowfall.  We’ve seen these pop up several times this Fall into Winter.  It appears another Stratospheric warming event is taking place in the Arctic regions(upper level temps warm and press lower level cold south), so we should see very cold temperatures the last few days of January and into February.

NAM model depiction for tomorrow night at 7PM. The green area represents light rain transitioning to light snow. Note the blue 5000ft freezing line(credit to Raleighwx.net).

 

DGEX(extended NAM) model(credit to Raleighwx.net) for 1pm on Tuesday. Green is moderate rain(possibly freezing rain in NC, NE GA, and NW SC). Top map shows temperatures. Notice the 30’s in NC, upstate SC and NE Georgia. This is what an insituational CAD, or cold air damming event looks like. Notice the warmer temperatures all around. The cold air is funneling down into these areas along the east slope of the Appalachians. Typically, these temps will be overstated by a few degrees, considering Arctic air is located to the NE:

 

 

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Pattern Change or not??? Where is Winter????

Continuing from my last post, the sharp trough that I anticipated to take place this week did form. Temperatures dropped into the teens with high temps in the 20’s and 30’s for one day, but the trough was not deep/sharp enough and tilted enough to form the cutoff upper level low the European model was forecasting. The result was rain followed by sharply cold temperatures for a couple days, with a light coating of snow in North Georgia and snow in the Appalachians.  Since then, the mild Winter of 2011/2012 continues…………why, and where do we go from here??

A strong vortex of low pressure continues to dominate the Alaskan landscape, bringing them bitterly cold air. Typically, if Alaska is cold, we aren’t. Why? That means the cold air is bottled, and has no way to be steered in our direction due to the counter clockwise flow around the strong vortex. In order to have that air transported our way, we need a strong area of high pressure, with clockwise flow, to get in place in or near Alaska.  That would funnel the cold into the United States. Also, Greenland has stayed very cold for similar reasons.  The latest European and GFS models are showing high pressure building into or near these areas in the next 7-10 days. With continued +PNA(roller coaster) setting up a ridge in the western US, this will eventually funnel the cold into the United States. The Arctic Oscillation, which basically tells us how cold the Arctic regions are at upper levels(+AO) is trending downward, and there are signs of a strong negative index very soon.  This would warm the stratosphere there and bring the cold down into the United States, as the upper level warm air presses the lower level cold out and to the south.  The NAO is trending negative to neutral, which could slow any systems that come through our area in the next 7-10 days(see attachments for AO, PNA and NAO courtesy of CPC).

What all this means is that IF the models are to be trusted(and after being locked in this pattern since November the likelihood is high for change), we should see very cold weather come into our picture for the SE US the end of next week(Thursday) following the strong upper level low that may give us up to 2 inches of rainfall Tuesday-Wednesday.  This cold air should be reinforced after a brief warmup, and IF the atmospheric setup changes as noted, we can expect a potentially bitterly cold arctic outbreak around January 20th. 

The Canadian model(see attached, courtesy of CMC) is showing an area of low pressure developing in the Gulf of Mexico next Thursday, moving to the Mid-Atlantic coast next Friday, possibly bringing us snow and ice, following the passage of the upper level low and an associated Arctic front, next Wednesday.  The European showed this low pressure area on last night’s run.  The setup supports this, and I will follow this over the next few days, and keep you advised. Hopefully our first “real” snow threat looms soon.

Ensemble Mean AO Outlook

Ensemble Mean NAO Outlook

Ensemble Mean PNA Outlook

 

 

 

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Pattern Change, Finally???? Historic storm for south and east coast showing up on models.

My Winter forecast included a colder than normal December through mid January, but that has obviously been a BIG error.  December temperatures have run five degrees above normal. What’s been driving that is the lack of a -NAO and -AO. This is partially due to a powerful low pressure vortex that has been anchored in or near the Gulf of Alaska, and the inability of the Madden Julian Oscillation(eastward moving tropical disturbance in the Indian & Pacific Ocean areas, that influences Eastern North America Wintertime temperatures) to move into the phase required.  Signs are now evident that the powerful vortex in Alaska will move to the west and southwest, and the MJO is moving into favorable phases to support a change in the weather pattern to the Wintry pattern I anticipated in December.  This would promote a transition to a -NAO and -AO, and much colder and stormier conditions COULD become locked in, just as the mild regime has been in place for several weeks.

Even in this mild pattern, one thing that has been in place recently, is a +PNA pattern, that has supported ridges in the western US. This index is forecast to strengthen, which would eventually lead to eastern US troughs. Currently, the European model and Canadian model are forecasting a monster trough amplification early next week, and the GFS shows the same configuration the following week. This is an obvious sign of the pattern change that is finally ongoing.  Will the change lock in or will the pattern revert back? I’m not sure, but I think the pattern should change to a more amplified(cold outbreaks and major storms) pattern for at least a few weeks, and possibly well into February.  Essentially, my Winter forecast would move forward one month, and the cold I anticipated from the beginning of December to the middle of January would occur from the beginning of January to the middle of February. 

Another aspect of the late Fall and early Winter, to this point, has been a prevalence of cut off upper level low pressure centers.  As the possible amplification(deep troughing in the eastern US – bottom of roller coaster) forms early next week, the European model forecasts a powerful cutoff low pressue system combining with a major cold outbreak. This would potentially result in a major snowstorm for the South, and up the Eastern US coastline.  The GFS model is showing the same amplification a week later. Please see attached links for images.  If this amplification takes place, the mild early Winter we have experienced will be a faint memory……….

Note the (7) contour(height/pressure circles) upper level closed low on the European forecast for hour 192(next Wednesday morning). This would pull down very cold air from the upper atmosphere in conjunction with Arctic air being brought down by a strong area of high pressure dropping down from Canada. On the colored image, notice the very cold temperatures(-10 to -15 C) at the 5000 foot level. This would mean very cold surface temperatures(teens and twenties F). In combination with this, I would anticipate an area of low pressure to develop in the Gulf of Mexico and move northeast near the Georgia/South Carolina coastline, bringing the potential for snow. The details will become clearer over the next few model runs.  Obviously, this could completely change, but the amplification the model shows is likely sometime within the next 7-10 days. Maybe not this dramatic, but something similar. Could just mean a change to cold temperatures, or could be much more Wintry! I’ll keep you updated.

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